BMW and Hyundai urged the US not to impose tariffs on auto imports, joining General Motors in pressing their case to the Commerce Department even as a top aide to President Donald Trump dismissed the concerns as “smoke and mirrors”.

“It seems that the threat to impose these sanctions is designed to achieve certain goals,” German newspaper Welt am Sonntag reported, citing a copy of BMW’s letter to Commerce Secretary Wilbur Ross. The Munich-based luxury automaker said its investment of almost US$9 billion in the Spartanburg, South Carolina, BMW plant, supports more than 120,000 US jobs.

Hyundai said the duties would be “devastating” to the Seoul-based automaker and jeopardise its plans to expand manufacturing in the US In comments to the Commerce Department, it also said weakening South Korea’s Hyundai would ultimately hurt Trump’s effort to halt North Korea’s nuclear ambitions.

White House trade adviser Peter Navarro earlier addressed Friday’s stern warning by GM to the Trump administration on Friday, that it could shrink US operations and cut jobs if tariffs are broadly applied to imported vehicles and auto parts.

“Increased import tariffs could lead to a smaller GM, a reduced presence at home and risk less – not more – US jobs,” the nation’s largest automaker said in comments submitted Friday to the Commerce Department.

That such a blunt statement came from GM – a company run by a CEO, Mary Barra, whose normal tack is to avoid the political fray and let trade groups address the president’s policies – was surprising to industry observers.

And it underscored how high she, and many industrial leaders, believe the stakes are as the president sinks the US into tit-for-tat trade squabbles across the globe. GM’s public pronouncement follows similar moves by Harley-Davidson Inc., Toyota Motor Corp. and Daimler AG.

The “comment suggests how severe the impact would be to GM, its employees and consumers,” said Michelle Krebs, analyst with AutoTrader.com. “There is a lot at stake for GM, the auto industry and the overall economy.”

Navarro shot back at GM on Saturday in an interview on CNN, saying the auto company was using “smoke and mirrors” to deceive the public. He said the impact of tariffs on the price of a GM car was equivalent to “a luxury floor mat.”

“Even the GM cars built here, about half the content is foreign,” Navarro said, adding that US factories had become “assembly plants” stitching together components made elsewhere. In the case of BMW’s massive South Carolina operation, that would be about 1,900 vehicles each day, many of which are exported.

Navarro added that Trump, having passed a tax cut that helps companies like GM and Harley, “felt betrayed” when they then threatened to move production jobs outside the US in response to the retaliatory actions of foreign countries to Trump’s tariffs.

In an interview with Maria Baritromo that aired Sunday morning on Fox News’s Sunday Morning Futures, Trump said his political supporters are a close mirror of Harley’s customer base – and they are unhappy with any plan to expand overseas production. “Harley is an American bike” and “they should build them in this country,” he said.

Trump ordered an investigation of whether auto imports pose national security risks last month under a section of the same 1960s trade law used to impose levies on steel and aluminium. The administration is said to be considering auto tariffs of as much as 25 per cent.

In Sunday’s interview with Fox, Trump said the tariffs are needed in part because of the European Union’s barriers to US-built vehicles. “The European Union is possibly as bad as China, just smaller,” Trump said. “They send a Mercedes in, we can’t send our cars in.”

Trump told reporters aboard Air Force One on Friday afternoon that he expected the Commerce Department to complete the investigation “in three or four weeks.”

Under the trade statute, Ross has until February to conclude the inquiry. But people familiar with the matter said Trump wants the investigation to be finished before the midterm elections in November so he can use the tariffs to his political advantage.

The investigation has raised alarm among manufacturers, parts suppliers and auto retailers because all major carmakers – including GM and Ford Motor Co. – import a substantial share of the vehicles they sell in the US from other countries.

Levies on parts also would have major implications for top models like the Ford F-150 pickup and Toyota Camry saloon by boosting prices by thousands of dollars.

GM fell 2.8 per cent – to US$39.40 – in New York on Friday, and has now posted three straight weekly declines, the longest such streak since March.

GM’s message came as a surprise because the company has kept close contact with the Trump administration, James Albertine, analyst with Consumer’s Edge Research said.

“So this came as a little bit of a shock to us,” he said, “as we thought they were working more along the lines of making sure the administration knows the severity of the impact tariffs would have.”

Barra had earlier tried to stay on good terms with Trump. She continued to serve on his Strategic and Policy Forum even after many other CEOs, such as Walt Disney’s Bob Iger and Tesla’s Elon Musk, quit to protest Trump’s withdrawal from the Paris climate agreement last year.

The forum was disbanded in August following Trump’s tepid response to attacks by white supremacists in Charlottesville, Virginia.

Now, the Detroit-based maker of Chevrolet, Cadillac, Buick and GMC vehicles is warning that additional tariffs – on top of those recently slapped on steel, aluminium and Chinese products – could hurt GM and ultimately its customers.

Higher prices would crimp sales, particularly to less-affluent consumers, and reduce the number of factory workers needed, it said.

If GM were to try to absorb the additional costs, it would have less money to invest in popular vehicles that sustain manufacturing jobs, or toward pivotal technologies including electric and self-driving cars.

“The threat of steep tariffs on vehicle and auto component imports risks undermining GM’s competitiveness against foreign auto producers by erecting broad brush trade barriers that increase our global costs, remove a key means of competing with manufacturers in lower-wage countries, and promote a trade environment in which we could be retaliated against in other markets,” the company said.

GM’s Chevrolet Silverado pickup was the top-selling model imported from Mexico last year, while the Chevrolet Equinox crossover was the leading vehicle sourced from Canada, according to LMC Automotive.

Just last week, GM announced plans to bring back the Chevy Blazer SUV later this year. The iconic American brand will be built at a plant in Mexico, a move that sparked angry comments from the United Auto Workers union.